org.apache.hudi.org.apache.hadoop.hbase.io.hfile.bucket.SharedMemoryMmapIOEngine Maven / Gradle / Ivy
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*
* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.hadoop.hbase.io.hfile.bucket;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.apache.hadoop.hbase.io.hfile.Cacheable;
import org.apache.yetus.audience.InterfaceAudience;
/**
* IO engine that stores data in pmem devices such as DCPMM. This engine also mmaps the file from
* the given path. But note that this path has to be a path on the pmem device so that when mmapped
* the file's address is mapped to the Pmem's address space and not in the DRAM. Since this address
* space is exclusive for the Pmem device there is no swapping out of the mmapped contents that
* generally happens when DRAM's free space is not enough to hold the specified file's mmapped
* contents. This gives us the option of using the {@code MemoryType#SHARED} type when serving the
* data from this pmem address space. We need not copy the blocks to the onheap space as we need to
* do for the case of {@code ExclusiveMemoryMmapIOEngine}.
*/
@InterfaceAudience.Private
public class SharedMemoryMmapIOEngine extends FileMmapIOEngine {
// TODO this will support only one path over Pmem. To make use of multiple Pmem devices mounted,
// we need to support multiple paths like files IOEngine. Support later.
public SharedMemoryMmapIOEngine(String filePath, long capacity) throws IOException {
super(filePath, capacity);
}
@Override
public boolean usesSharedMemory() {
return true;
}
@Override
public Cacheable read(BucketEntry be) throws IOException {
ByteBuffer[] buffers = bufferArray.asSubByteBuffers(be.offset(), be.getLength());
// Here the buffer that is created directly refers to the buffer in the actual buckets.
// When any cell is referring to the blocks created out of these buckets then it means that
// those cells are referring to a shared memory area which if evicted by the BucketCache would
// lead to corruption of results. The readers using this block are aware of this fact and do
// the necessary action to prevent eviction till the results are either consumed or copied
return be.wrapAsCacheable(buffers);
}
}